This application is based on and claims priority under 35 U.S.C. xc2xa7119 with respect to a Japanese Patent Application 2001-084262, filed on Mar. 23, 2001, the entire content of which is incorporated herein by reference.
This invention generally relates to a displacement sensor or a displacement sensor structure. More particularly, this invention pertains to a non-contact type displacement sensor structure or an angle displacement sensor structure. Further, this invention relates to a displacement sensor preferably applied to an accelerator pedal sensor.
Various sensor structures have been known already. A non-contact type displacement sensor for detecting a displacement of angle by using a hall element or a magnetic resistor is disclosed, for example, Japanese Patent Laid-Open Publications No. 8 (1996)-68606 and 2 (1990)-122205.
Referring to FIG. 9, a sensor body 22 disclosed in the former Japanese Patent Laid-Open Publication No. 8 (1996)-68606 is formed of a housing 21 having an IC containing portion 241 containing a hall element and a casing 13 for supporting an input shaft 14. The input shaft 14 is connected to a rotational member 15 for supporting magnets 171, 172 and a yoke 16. The magnets 171, 172 form a magnetic field interacting with the hall element. The input shaft 14 and the rotational member 15 are completely independent members from each other. The rotational member 15 is connected to the input shaft 14 as an external connecting member. Therefore, the magnets 171, 172 and the yoke 16 supported by the rotational member 15 are also completely independent members which are present outside the input shaft 14. The yoke 16 to which the magnets 171, 172 are attached is secured to the rotational member 15 by means of a screw.
A peninsular portion 211 including the IC containing portion 241 is formed in the housing 21 so as to intersect with the parallel magnetic field produced by the magnets 171, 172. In such a case, the hall element (the magnetic sensing element) is required to be accurately located at a position in which the distortion of the magnetic field can be reduced as much as possible, i.e., at a position on a central axis of the input shaft 14, so as to detect the magnetic field with a high level of accuracy.
Referring to FIG. 10, according to the sensor disclosed in the latter Japanese Patent Laid-Open Publication No. 2(1990)-122205, a rotational shaft 2 having a small diameter is provided with a large diameter portion having a diameter nearly twice as large as the rotational shaft 2 at a tip end portion thereof. The large diameter portion is employed as a magnetic holder 22 in which permanent magnets 3A, 3B are disposed. A hall element 5 (a magnetic sensing element) is disposed in a cylindrical space which is enclosed by the permanent magnets 3A, 3B and has approximately the same diameter as the diameter of the rotational shaft 2. The space in the rotational shaft 2 is in a filled structure (i.e., a solid structure) except for the space where the hall element 5 is disposed.
However, according to the former described sensor in which the yoke 16 is secured to the rotational member 15 by the screw, the rotational member 15 and the yoke 16 are required to be large-sized in order to assure a space for fixing them to each other. The size of the sensor main body 22 itself is hence increased, as well. This may lead to an increase of cost expended on each component. Further, the yoke 16 and the magnets 171, 172 are externally connected to an end portion of the input shaft 14 via the rotational member 15. Therefore, those components may be required to be large-sized in each width direction. The sensor main body 22 is hence required to be large-sized, as well.
As described above, the hall element (the magnetic sensing element) is required to be positioned on the central axis of the input shaft 14 and on a central position of the magnetic field having small distortion so as to detect the magnetic field with a high level of accuracy. However, the input shaft 14, the rotational member 15, the yoke 16 and the magnets 171, 172 exist and are assembled as members independent from one another. Therefore, position detecting of each component with a high level of accuracy may be difficult due to size fluctuation of each component or dimensional errors for assembly each component.
On the other hand, according to the latter described sensor, the housing 1 for supporting the rotational shaft 2 is required to include a complicated inner structure due to the small diameter of the rotational shaft 2. When the sensor is applied to an automotive vehicle or the like, vibration may occur affecting the accuracy of detection of a rotational angle of the magnetic field.
Further, the rotational shaft 2 is required to be light in weight and have a large surface area so as to perform a delicate control of the rotation of the rotational shaft 2 under a simple structure. However, the rotational shaft disclosed in the latter publication is the solid structure, which is not a hollow structure, and has the small diameter. Therefore, a mechanism for controlling the rotational shaft 2 may be required to be complicated. As illustrated in FIG. 10, there is a large unnecessary space in the sensor. The entire size of the housing of the sensor may become unnecessarily large.
Accordingly, the above disclosed sensors are still subject to certain improvements with respect to accurately determining a position of a magnetic sensing element in a magnetic field, a downsizing of the sensor, and providing a displacement sensor for performing a delicate control of a rotational shaft of the sensor under a simple structure.
According to the present invention, a non-contact type displacement sensor is provided with a housing, a rotational shaft being in an approximately cylindrical hollow shape, a magnetic circuit forming member disposed in an inner space of the rotational shaft, and a magnetic sensing element supported by a housing so as to be positioned on a central axis of the rotational shaft in a space enclosed by the magnetic circuit forming member, wherein the magnetic sensing element is not displaced.